This invention relates to a semiconductor device and a method of manufacturing the semiconductor device and, in particular, relates to a semiconductor device having a gate insulating film on a semiconductor region containing SiC as a main component and to a method of manufacturing such a semiconductor device.
MOS devices using Si (silicon) are currently widely used as semiconductor devices, but have a drawback that the withstand voltage is low for use as power devices. Means is taken for increasing the length of a drift region and reducing its concentration in order to increase the withstand voltage. However, there is a limit to the withstand voltage that can be increased thereby. Further, there is a problem that the on-resistance increases thereby. In view of this, IGBTs using silicon have been commercialized, but there is a problem that the switching speed is slow. Accordingly, attention has been paid to SiC having a withstand voltage about ten times greater than that of silicon. In addition, if comparison is made with the same withstand voltage, the on-resistance is one hundredth to one five-hundredth of Si devices. Further, since the thermal conductivity of SiC is about 3.3 times greater than that of Si, it is also excellent as high-temperature operating devices. WO97/39476 (Patent Document 1) discloses a SiC element applicable to a semiconductor element of a high-power device, a high-temperature device, an environment-resistant device, or the like and a manufacturing method thereof.
For realizing a transistor of a MOS (metal/insulating film/semiconductor) structure using SiC, a gate insulating film thereof is required to have various high-performance electrical properties and high reliability characteristics such as low leakage current characteristics, low interface trap density, and high voltage resistance.
In order to establish a gate insulating film forming technique satisfying these requirements, use has conventionally been made of a thermal oxidation, wet oxidation technique using oxygen molecules or water molecules at about 1200° C. or more.
Conventionally, when a silicon oxide film is formed on the SiC surface using such a thermal oxidation, wet oxidation technique, since the interface trap density is extremely high as compared with a silicon oxide film on the silicon surface, the channel resistance increases. As a result, realization of a high-mobility high-performance SiC MOS transistor has been impeded. Specifically, SiC is hexagonal and thus has no plane corresponding to a (100) plane of silicon. When an insulating film is formed by the conventional heat treatment method, only the insulating film with extremely large interface states is obtained.
Various processes have been attempted for solving such a problem in the conventional thermal oxidation process. Among them, the technique described in Japanese Unexamined Patent Application Publication (JP-A) No. 2004-319907 (Patent Document 2) introduces an inert gas and gaseous oxygen molecules into a plasma to cause the inert gas having a large metastable level to efficiently perform atomization of the oxygen molecules, thereby oxidizing the silicon surface by atomic oxygen O radicals. This technique achieves, in silicon, the low leak current characteristics, the low interface trap density, and the high withstand voltage equivalent to those of the conventional thermal oxidation by irradiating a microwave to a mixed gas of krypton (Kr) being an inert gas and oxygen (O) to generate a mixed plasma of Kr and O2, thereby producing a large amount of atomic oxygen O radicals to carry out oxidation of silicon at a temperature of about 400° C. Further, according to this oxidation technique, a high-quality oxide film can also be obtained on the silicon surface having a plane orientation other than the (100) plane.